por cpl em 16/07/18

Informações sobre Chicote Elétrico - Cabos, Isolamento, Acabamento, Plugs

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(Electrical Wiring Information - Cables, Insulation, Sleeve, Terminal)


Without wire to conduct and protect electric flow, there is no point to discussing topics such as connectors and harness routing. So we will start here. In its basic form wire is compromised of a conductor and an insulator.

Anything but copper wire on an automotive application is a poor choice or an idea of over-grandeur. True, there are in fact better conductor materials than copper. In light of that, copper is still the better choice in terms of performance and cost value. Copper wire comes in both solid and stranded variants.

Try comparing the flexibility of solid and stranded wire of the same gauge (AWG). Stranded copper wire is preferred in applications that require flexibility, such as automotive harnesses. Solid wire is best left to your home electrical projects. Stranded copper also comes in tinned and non-tinned versions. Tinning seals off the conductor to protect from oxidation but does sacrifice some of its flexibility.

Contaminates can actually permeate the insulation and oxidize an unprotected conductor over time. Have you ever striped insulation off an older wire and seen that the copper strands have a black tint to them? This is a perfect example of this phenomenon.

That oxidation occurs as contaminates passed through the insulation and react with the conductor material. This oxidation degrades circuit function and alters the physical characteristics of the conductor. Some have commented that using tinned copper wire with crimped connector terminals leads to poor connections and should be avoided. The condition they are noting is stranded copper not conforming to the crimp nearly as well when tinned. Personally, this connection concern is not enough to avoid the extra oxidation protection of tinned wire. I would rather replace a bum connector terminal than an entire length of wire. Connection is hardly ever an issue as long as proper crimping procedures are used. In fact, tinned copper can tolerate re-crimping better than non-tinned copper. This is mostly due to non-tinned copper having some level of oxidation that limits the termination quality the second time around.
In reality the wiring in your Subaru is made up of plain stranded copper if you are interfacing the original wiring go with a stranded copper in GXL or TXL spec (see below). It could afford you some cost savings going this route.

Conductor size

American Wire Gauge (AWG) is the sizing standard used in the US for any electrical conducting wire. The AWG number designation is related mathematically to the diameter of a solid conductor or the total diameter of a stranded conductor. Stranded conductors will have some dead-air space between the strands due to its design. Due to this dead-air, stranded conductors will typically have a slightly larger “true” diameter than a solid conductor of the same AWG designation. You can look up the AWG – diameter mathematical relationship, but it probably will not impact any of your decision making. There are also other wire gauge standards used for non-conducting wires/cables. These are not interchangeable so avoid mixing any steel wire or music wire gauges into your electrical decisions.
There is also a metric sizing standard used for electrical conducting wire. The main difference is the metric designation will increase as wire diameter increases. The AWG standard is inverse of this; AWG designation will decrease as wire diameter increases. There are AWG – Metric equivalent charts to help convert between the two standards.

The standardization of wire sizes helps keep some consistency when selecting wire for your harnessing projects. The basic concept to remember is that larger diameter conductors have more current carrying capacity than smaller diameter conductors. Any more detail than this is not really useful for most DIY’ers.

AWG Selection
Circuits designed using a factor of safety is good practice. A 1.25-1.50 factor of safety will provide some extra wiggle room and ensure that the circuits can adequately carry the electrical load imparted on them. Knowing the maximum circuit current is a good starting point. Using the maximum current and multiplying by 1.25 will give you a design current. This design current is compared to the required circuit length on available wire gauge selection tables.

Remember that circuit length is not just the distance from the battery (+) to the load. You need to consider the ground lead as well. These selection charts will show you the smallest gauge (AWG) wire to use. Going to a smaller wire size is risky and not advisable. Obviously choosing a larger size is OK but partially wasteful and may provide routing/flexibility concerns.
MAX current x 1.25 (safety factor) = design current wire length => wire AWG selection

Wire must conduct electricity but it also must protect that electric signal. Insulation provides protection from electrical shorts, heat, chemicals, oxidation, abrasion, etc. Insulation also provides a labeling location and affects the overall wire flexibility. PVC insulation is common and more than adequate for in-cabin wiring. PVC has since been passed up with better materials such as Tefzel and Teflon. These offer an improved heat resistance which makes them better choices for wiring near heat sources such as in an engine bay. You can use it for in-cabin wiring but it is sort of overkill unless you are trying to keep some wire consistency throughout the vehicle.
Here are some typical grades of hook up wire:
GPT – (up to 80degC) extruded PVC insulation which will melt in the presence of heat
SXL – (up to 125degC) extruded and cross linked PVC has higher heat resistance
GXL – (up to 125degC) extruded and cross linked PVC has higher heat resistance, reduced insulation thickness for easy routing
TXL – (up to 125degC) extruded and cross linked PVC has higher heat resistance, further reduced insulation thickness for easy routing and lightweight

Beyond the PVC insulation hook up wire you will get into the military and aviation grades such as MIL-W-22759 unshielded and tinned stranded copper:
ETFE (Tefzel) – (ethylene.tetrafluorbethylene) (up to 150degC)
PTFE (Teflon) – (up to 200degC)
Raychem SPEC55 has long been the benchmark wire to use in racing harnesses. SPEC55 is pretty nice material to work with but availability/cost can be prohibitive for some and unnecessary for many. You can find some alternatives as long as you know what type of wire you are looking to.

Here you can see how different insulation materials hold up against contact with a heated soldering iron. The GPT insulation melts right away in comparison the Tefzel insulation ends up with some small scars.

Insulation Color
Insulation can come in many different colors and combinations. Black, red, white, purple, blue, yellow w/ blue stripe, translucent, tan, brown, etc. Different insulation colors can be used to identify specific or similar circuits. Multi-color harnesses will improve any repair and rework that may occur after the harness build.
This is great as long as you have the money and space to stock a multitude of different colored wires in the AWG sizes commonly used. This is where mono-color harnesses have an advantage of building a harness in only one insulation color regardless of AWG. This method greatly reduces your wire stock at the sacrifice of some wire identification.

Personally I think mono-color harnesses are more professional as long as an adequate labeling scheme is employed. An insulation printer is probably out of reach for most DIY’ers so other methods are more common:
- stick on circuit labels
- printed labels under clear shrink tubing

Harness sleeve
Even though covering a wire harness is not always required, it does provide protection from abrasion, cut-through, heat, chemicals, etc. Sleeves also offer some level of separation or grouping from other harnesses. There are many types of wire sleeve; some even fulfill a specific purpose.

PVC Tube

One of the lower cost wire sleeve options is PVC tubing. PCV tube offers chemical resistance and helps maintain the harness bundle. The only down side I have found with this type is when covering longer lengths of harness. The longer the sleeve the more resistance (friction) there is to push the wires through. I tend to use this at harness nodes and use another type of covering on the larger/longer sections.

Split looms (spiral and corrugated)

Probably the most common type and easiest to get at a local supply.

Expanding Braided Sleeve

Expandable braided sleeve is an easy to use harness building material. It is sometimes called sheathing, snake skin, scuff jacket, wire mesh, etc. There are a few different materials used to make braided sleeve. Polyethylene Terephthalate (PET) is by far the most common material. PET sleeve is often mislabeled as nylon sleeve. Genuine nylon sleeve costs more than PET, which helps identify impostors. PET provides better abrasion protection against rough surfaces. Nylon provides better abrasion protection against smooth surfaces and wet environments. There are also some metalized mylar materials available but that goes beyond the scope of our uses.
Braided sleeve usually comes rolled on a spool and will lay flat when unrolled. You may see a crease on either side of the sleeve as it is unrolled. Some manufacturers go through an extra process of rounding their braided sleeve. Rounding removes those creases, even if the sleeve is packaged on a spool. This can add to the cost but it does make for a nicer end product harness.
You may be thinking, will all of these fine threads what happens when you cut it to length. This stuff is going to fray out all over the place. There is more expensive braided sleeve that is treated with a resin to control fraying. It works but there are some lower cost alternatives to minimize fraying. Applying a section of shrink over the ends of the sleeve will help cap off the ends and control fraying. There are also nice harness jackets for sale that can cap off the ends similar to the shrink. Cutting braided sleeve with a hot knife will provide an end that will not require any covering or fray protection. A heat knife will run you about $100 but hey it’s a new tool right?

Thermal sleeve

Usually this consists of a fiberglass inner wrap surrounded by a high temp silicon coating. I have used this for years to protect AN turbo drains that reside close to exhaust down pipes.


Alternatively a harness could be wrapped in a good electrical tape or specific harness tape. I prefer the cloth harness tapes as they will leave less sticky adhesive behind. Ever gone back to see what electrical tape used as a harness wrap looks like? That is a mess. Using tape is alright but just think what you may need to unwrap to perform any repair or modifications. I tend to leave this to smaller harness sections or nodes, areas that I am very confident I will not have to get back into later on.

Cable ties could also be used but use care when cutting off the excess tie. I think most of us have reached into a tight engine bay and drawn blood on a sharp cable tie at least once.

Connectors – The parts that connect your wires. Yep, I'm using Deutsch connectors for the example photos. Most of this info can be applied to other connector brands.


Stamped or solid terminals pins/sockets
Connector terminals may be offered in stamped and solid types. Stamped terminals are usually the more common horseshoe termination and can have a few sizes to cover different AWG ranges. Obviously you should use terminals with an AWG range that matches the wire AWG.
Solid terminals are not as DIY’er common, cost more, and require an expensive barrel crimper. A 4 prong barrel crimper is more fool proof than a 3 prong. Solid terminals can come in a few AWG ranges; the crimper is adjusted to the AWG wire you are using. The advantage of solid terminals is a stronger barrel termination and less connection resistance than stamped terminals. These advantages are probably more useful for a professional harness builder rather than a DIY’er. In the end use whichever type you prefer.

Terminal Plating
Plating controls terminal corrosion and cycle life. There are numerous plating metals with varied properties and applications. Intermixing of plated terminals (ex. nickel pin into gold socket) is not suggested, although they will typically work fine under favorable conditions. In humid or wet conditions, galvanic oxidation between dissimilar terminals will lead to connection faults. Nickel and gold are the more common plating offerings.
Nickel plating is best used on most circuits you will encounter while wiring you car. This will mostly consist of any pwr supply, gnd supply, sensor signals, control signals, etc.
Non plated or tin terminals have less corrosion resistance but can perform quite well in most automotive applications.
Gold plating is best reserved for sensitive circuits such as multiplexing, Vref, and critical circuits. Honestly a DIY’er will not usually deal with sensitive circuits so this is not of much concern. Gold plating offers improved durability, contact consistency/durability, and lower insertion force. Gold plated terminals obviously cost more than nickel plated terminals, so design your harness with purpose and cost in mind. You will not get any benefit from using gold terminals if unneeded.

Gold plating like any plating can vary in applied thickness. Some general gold plating is no more than a wash coat and serves very little advantage over cheaper plating metals. This just allows the retail price to be increased. Functional gold plating is thicker and does provide advantages. Most good quality terminals will be of a sufficient gold plating thickness. Plating types can go on and on. For example platinum and rhodium are the next step up from gold, but I doubt you would want to purchase these to wire up your new gauges or a turbo timer.

Terminal Crimping
Stamped pins/sockets use a common crimp style that most of us have seen before. Correct crimping is two crimps using the proper crimping tool. A crimp is placed on the wire conductor and one on the insulation. The first crimp contacts the conductor and serves as the electrical connection. The second crimp contacts the insulation and serves as a strain relief.

Solid pins/sockets use a barrel crimp style. Correct crimping is one crimp using a proper crimping tool. This crimp contacts the wire conductor and serves as the electrical connection. There is no second crimp used for strain relief. Some connector bodies have features that will provide strain relief, usually if you are using solid terminals you are inserting them into premium connector bodies that provide some built-in strain relief. Additional strain relief could be provided with heat shrink tubing.

Connector function is only as good as the applied termination. The proper termination style may be different between terminal types and could require entirely different crimping tools. Always use and solid crimp with the correct crimping tools….never solder.
These comments will surely be met with some resistance. As far as I know soldering terminals is not recommended by any manufacturer. Soldering after applying a proper crimp is also not recommended. Soldering wicks through the conductor and reduces wire flexibility. This makes soldered connections more prone to vibration fatigue. A proper solid crimp is the most reliable method. In the end, connection reliability is dependent on the quality procedure used. I've seen soldered terminations live well.......and crimped terminations fail.

If you MUST solder a crimped terminal, lightly tin the wire (if not already tinned). Apply a proper crimp with the correct tools, then pull test for a sound crimp. Once the crimp is completed, heat the conductor crimp area with a soldering iron. This will re-melt the tinned conductor and flow out under the crimp. Adding extra solder is not recommended. You may need to follow up with a re-crimp. Do one last pull test to make sure everything is good to go.

Always pull test your terminations!